High voltage power supply

ABSTRACT

A power supply for transmitting voltage to a device, comprising: a web including a piezoelectric exterior layer for generating a voltage on the surface thereof in response to being deformed; and means for transferring the voltage on the surface of said piezoelectric exterior layer to the device is disclosed.

The present invention relates generally to a power supply primarily foruse in reproduction systems of the xerographic, or dry copying, moreparticularly, concerns a power supply for supplying high voltage at lowcurrent levels to charging devices.

Generally, the process of electrostatographic copying is initiated byexposing a light image of an original document onto a substantiallyuniformly charged photoreceptive member. Exposing the chargedphotoreceptive member to a light image discharges a photoconductivesurface thereon in areas corresponding to non-image areas in theoriginal document while maintaining the charge in image areas, therebycreating an electrostatic latent image of the original document on thephotoreceptive member. This latent image is subsequently developed intoa visible image by depositing charged developing material onto thephotoreceptive member such that the developing material is attracted tothe charged image areas on the photoconductive surface. Thereafter, thedeveloping material is transferred from the photoreceptive member to acopy sheet or to some other image support substrate to create an imagewhich may be permanently affixed to the image support substrate, therebyproviding an electrophotographic reproduction of the original document.In a final step in the process, the photoconductive surface of thephotoreceptive member is cleaned to remove any residual developingmaterial which may be remaining on the surface thereof in preparationfor successive imaging cycles.

The electrostatographic copying process described hereinabove is wellknown and is commonly used for light lens copying of an originaldocument. Analogous processes also exist in other electrostatographicprinting applications such as, for example, digital laser printing wherea latent image is formed on the photoconductive surface via a modulatedlaser beam, or ionographic printing and reproduction where charge isdeposited on a charge retentive surface in response to electronicallygenerated or stored images.

As discussed above, in electrostatographic reproductive devices it isnecessary to charge a suitable photoconductive or reproductive surfacewith a charging potential prior to the formation thereon of the lightimage. Various devices have been proposed for the application of theelectrostatic charge or charge potential to the photoconductiveinsulating body of Carlson's invention; one method of operation employs,for charging the photoconductive insulating layer, a form of coronadischarge wherein an adjacent electrode comprising one or more fineconductive bodies maintained at a high electric potential causesdeposition of an electric charge on the adjacent surface of thephotoconductive body. Examples of such corona discharge devices aredescribed in U.S. Pat. No. 2,836,725, to R. G. Vyverberg and U.S. Pat.No. 2,922,883, to E. C. Giamio, Jr. In practice, one corotron (coronadischarge device) may be used to charge the photoconductor beforeexposure and another corotron used to charge the copy sheet during thetoner transfer step. Corotrons are cheap, stable units, but they aresensitive to changes in humidity and the dielectric thickness of theinsulator being charged. Thus, the surface charge density produced bythese devices may not always be constant or uniform.

The operation of transferring developing material from thephotoreceptive member to the image support substrate is realized at atransfer station. In a conventional transfer station, transfer isachieved by applying electrostatic force fields in a transfer regionsufficient to overcome forces holding the toner particles to the surfaceof the photoreceptive member. These electrostatic force fields operateto attract and transfer the toner particles over to the copy sheet orother image support substrate. Typically, transfer of toner imagesbetween support surfaces is accomplished via electrostatic attractionusing a corotron or other corona generating device. In such coronainduced transfer systems, the surface of the image support substrate isplaced in direct contact with the toner image while the image issupported on the photoreceptive member. Transfer is induced by"spraying" the back of the support substrate with a corona dischargehaving a polarity opposite that of the toner particles, therebyelectrostatically attracting the toner particles to the sheet. Anexemplary corotron ion emission transfer system is disclosed in U.S.Pat. No. 2,836,725.

Toner transfer and charging has also been accomplished successfully viabiased roll transfer systems. This type of transfer apparatus was firstdescribed by Fitch in U.S. Pat. No. 2,807,233, which disclosed the useof a metal roll coated with a resilient coating having an approximateresistivity of at least 10⁶ ohm-cm, providing a means for controllingthe magnetic and non-magnetic forces acting on the toner particlesduring the transfer process. Bias roll transfer has become the transfermethod of choice in many state-of-the-art xerographic copying systemsand apparatus, as can be found, for example, in the Model 9000 Series ofmachines manufactured by Xerox Corporation. Notable examples of biasroll transfer systems are described in U.S. Pat. No. 3,702,482 by C.Dolcimacsolo et al, and U.S. Pat. No. 3,782,205, issued to T. Meagher.Other general examples of bias roll transfer systems can be found inU.S. Pat. Nos. 3,043,684; 3,267,840; 3,328,193; 3,598,580; 3,525,146;3,630,5911, 3,684,364; 3,691,992; 3,832,055; and 3,847,478, amongothers.

Hereinbefore, transfer and charging systems have required sources ofhigh voltage at low current levels for charging reproductive surfacewith a charging potential prior to the formation thereon of the latentimage, and thereafter maintaining the same pattern and intensity ofelectrostatic fields for charging as on the latent image beingreproduced to induce transfer onto a copy sheet. This requirement hasbeen usually met by incorporating high voltage power supplies forfeeding the coronas and bias rolls which perform such processes asprecharge, charge development and transfer. These high voltage powersupplies have added to the overall cost and weight ofelectrophotographic printers.

A simple, relatively inexpensive, and accurate approach to eliminatingthe expense and weight of traditional high voltage sources in suchprinting systems has been a goal in the design, manufacture and use ofelectrophotographic printers. The need to provide accurate andinexpensive transfer and charging systems has become more acute, as thedemand for high quality, relatively inexpensive electrophotographicprinters has increased.

SUMMARY OF THE INVENTION

Pursuant to an aspect of the invention there is provided a power supplyfor supplying power to a device which includes an endless web having apiezoelectric exterior layer for generating a voltage on the surfacethereof in response to said piezoelectric exterior layer being deformed.Means are provided for transferring the voltage on the surface ofpiezoelectric exterior layer to the device.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention will become apparentfrom the following description in conjunction with the accompanyingdrawings, in which:

FIG. 1 illustrates the power supply of the present invention in atypical electrostatographic printing machine.

FIG. 2 illustrates an enlarged view of power supply of the presentinvention;

FIGS. 3 illustrate other embodiments of the present invention;

FIG. 4 illustrates the geometry of a piezoelectric sheet;

FIG. 5 illustrate a Xeromorph (bimorph) sheet which is utilized by thepresent invention; and

FIG. 6 illustrate a Xeromorph (unimorph) sheet which is utilized by thepresent invention.

As indicated hereinabove, the present invention provides a novel powersupply for use in an electrostatographic printing machine. While thepresent invention will be described with reference to a preferredembodiment thereof, it will be understood that the invention is notlimited to this preferred embodiment. On the contrary, it is intendedthat the present invention cover all alternatives, modifications, andequivalents as may be included within the spirit and scope of theinvention as defined by the appended claims. Other aspects and featuresof the present invention will become apparent as the descriptionproceeds.

Referring now to the drawings, where the showings are for the purpose ofdescribing a preferred embodiment of the invention and not for limitingsame, the various processing stations employed in the reproductionmachine illustrated in FIG. 1 will be described only briefly. It will nodoubt be appreciated that the various processing elements also findadvantageous use in electrophotographic printing applications from anelectronically stored original.

The exemplary electrophotographic reproducing apparatus of FIG. 1employs a drum 10 including a photoconductive surface 12 deposited on anelectrically grounded conductive substrate 14. A motor (not shown)engages with drum 10 for rotating the drum 10 to advance successiveportions of photoconductive surface 12 in the direction of arrow 16through various processing stations disposed about the path of movementthereof, as will be described.

Initially, a portion of drum 10 passes through charging station A. Atcharging station A, a charging structure in accordance with the presentinvention, indicated generally by reference numeral 20, charges thephotoconductive surface 12 on drum 10 to a relatively high,substantially uniform potential. This charging device will be describedin detail hereinbelow.

Once charged, the photoconductive surface 12 is advanced to imagingstation B where an original document (not shown) is exposed to a lightsource for forming a light image of the original document which isfocused onto the charged portion of photoconductive surface 12 toselectively dissipate the charge thereon, thereby recording anelectrostatic latent image corresponding to the original document ontodrum 10. One skilled in the art will appreciate that a properlymodulated scanning beam of energy (e.g., a laser beam) may be used toirradiate the charged portion of the photoconductive surface 12 forrecording the latent image thereon.

After the electrostatic latent image is recorded on photoconductivesurface 12, drum 10 is advanced to development station C where amagnetic brush development system, indicated generally by the referencenumeral 30, deposits developing material onto the electrostatic latentimage. The magnetic brush development system 30 includes a singledeveloper roller 32 disposed in developer housing 34. Toner particlesare mixed with carrier beads in the developer housing 34, creating anelectrostatic charge therebetween which causes the toner particles tocling to the carrier beads and form developing material. The developerroller 32 rotates to form a magnetic brush having carrier beads andtoner particles magnetically attached thereto. As the magnetic brushrotates, developing material is brought into contact with thephotoconductive surface 12 such that the latent image thereon attractsthe toner particles of the developing material, forming a developedtoner image on photoconductive surface 12. It will be understood bythose of skill in the art that numerous types of development systemscould be substituted for the magnetic brush development system shownherein.

After the toner particles have been deposited onto the electrostaticlatent image for development thereof, drum 10 advances the developedimage to transfer station D, where a sheet of support material 42 ismoved into contact with the developed toner image via a sheet feedingapparatus (not shown). The sheet of support material 42 is directed intocontact with photoconductive surface 12 of drum 10 in a timed sequenceso that the developed image thereon contacts the advancing sheet ofsupport material 42 at transfer station D. A charging device 40 isprovided for creating an electrostatic charge on the backside of sheet42 to aid in inducing the transfer of toner from the developed image onphotoconductive surface 12 to a support substrate 42 such as a sheet ofpaper. While a conventional coronode device is shown as chargegenerating device 40, it will be understood that the various chargingdevice as discussed supra, can be substituted for the corona generatingdevice 40 for providing the electrostatic charge which induces tonertransfer to the support substrate materials 42. The support material 42is subsequently transported in the direction of arrow 44 for placementonto a conveyor (not shown) which advances the sheet to a fusing station(not shown) which permanently affixes the transferred image to thesupport material 42 creating a copy or print for subsequent removal ofthe finished copy by an operator.

Invariably, after the support material 42 is separated from thephotoconductive surface 12 of drum 10, some residual developing materialremains adhered to the photoconductive surface 12. Thus, a finalprocessing station, namely cleaning station E, is provided for removingresidual toner particles from photoconductive surface 12 subsequent toseparation of the support material 42 from drum 10. Cleaning station Fcan include various mechanisms, such as a simple blade 50, as shown, ora rotatably mounted fibrous brush (not shown) for physical engagementwith photoconductive surface 12 to remove toner particles therefrom.Cleaning station F may also include a discharge lamp (not shown) forflooding the photoconductive surface 12 with light in order to dissipateany residual electrostatic charge remaining thereon in preparation for asubsequent imaging cycle. As will be described, the present inventionmay also be utilized as a substitute for such a discharge lamp tocounter any residual electrostatic charge on the photoconductive surface12.

The foregoing description should be sufficient for purposes of thepresent application for patent to illustrate the general operation of anelectrophotographic reproducing apparatus incorporating the features ofthe present invention. As described, an electrophotographic reproducingapparatus may take the form of any of several well known devices orsystems. Variations of the specific electrostatographic processingsubsystems or processes described herein may be expected withoutaffecting the operation of the present invention.

Referring now more particularly to FIGS. 2 and 3 and to the specificsubject matter of the present invention, preferably, charging device 20is an ionomorphic charging device as disclosed in ferrofluid mediacharging of photoreceptors, U.S. application Ser. No. 08/250,090. Theprimary components of the fluid media charging structure 20 are a fluidreservoir 22 for placing the fluid media 24 in contact with thephotoconductive surface 12 of the drum 10, and a voltage power supply 26of the present invention coupled to the fluid reservoir 22 for applyinga DC voltage bias to the fluid media 24.

In the embodiment of FIG. 2, the fluid reservoir 22 comprises a simplebeaker or other vessel for containing an ionically conductive fluidmedia 24. A conductor 28, such as a copper wire, is coupled to a voltagepower supply 26 of the present invention and is contacted with the fluidmedia 24 in order to apply an ion producing bias voltage to the fluidmedia 24. Contact between the fluid media 24 and the conductor 28 may befacilitated by a conductive nipple 21 extending into reservoir 22 andcapable of being coupled to conductor 28. Alternatively, the fluidreservoir 22 may include a container fabricated of brass, stainlesssteel or any other conductive material or conductive composite materialssuch as a carbon loaded polymer or plastic, wherein a conductor ismerely placed in contact with the fluid reservoir (as shown in FIG. 2)in order to apply a voltage bias to the fluid media. The conductivity ofthis conductive fluid reservoir can be as low as about 2 nano-mho/cm.Thus, electrical contact can be made the ionically conductive fluideither by immersing a wire or other electrical contact element into thefluid if the fluid reservoir 22 is made of an electrically insulatingmaterial (as shown in FIG. 1), or by applying a biasing voltage directlyto the fluid container if the fluid reservoir 22 is made of a conductivematerial (as shown in FIG. 2).

Examples of ionically conductive liquid which may serve as the fluidmedia 24 include any liquid based material capable of conduction ofions, including simple tap water and even distilled deionized water (theconductivity thereof believed to be caused by the known dissolution ofcarbon dioxide in water). Components which can be added to the water torender it more ionically conductive include atmospheric carbon dioxide(CO₂), lithium carbonate, sodium carbonate, potassium carbonate, sodiumbicarbonate and the like. The concentration ranges can vary from tracelevels to saturation. Another example of an ionically conductive mediumis a gel that is composed of 4 wt % acrylic acid neutralized with NaOHcontaining 96 wt % water. Numerous other fluid compounds and materialswhich may be desirable for use and are described in commonly assignedpatent application Ser. No. 08/250,749.

The ionically conductive fluid may be contacted to the imaging member inseveral ways. The fluid itself may be directly contacted with thephotoreceptor surface by merely filling the fluid reservoir 22 to itsmaximum capacity such that a meniscus is formed just above the upperperimeter of the reservoir 22, allowing the fluid media 24 to impingeupon the surface of the photoreceptor through an opening in thecontainer reservoir. In this embodiment, selective contact between thethe fluid media and the photoreceptor surface may be accomplished byselectively positioning the reservoir into and out of close proximitywith the photoreceptor.

Numerous alternative means for contacting the fluid media to thephotoreceptor may also be contemplated. One such alternative will bediscussed in greater detail with respect to FIG. 2, wherein the fluidmedia 24 includes a ferrofluid of the type which exhibits an internalmagnetic moment which can be spontaneously organized in a commondirection under the influence of magnetic fields such that the positionof the ionic conductive fluid media can be controlled via magneticfields. In this alternative embodiment, the fluid media 24 comprises aferrofluid material which is located within a reservoir having a smallopening or aperture 23, wherein the aperture 23 is positioned oppositethe imaging member 10. Preferably aperture 23 is provided in the form ofa small slit which serves to confine the area of contact between thefluid media and the photoreceptor, and also serves to minimize theevaporation of the fluid from the reservoir. A magnet 29 is provided inthe vicinity of the reservoir for controlling the position of theferrofluid. In the illustrated embodiment, an electromagnet coupled to abiasing source 27 via switch 25 is positioned external to the reservoir22 positioned opposite the aperture 23, separated from the reservoir 22by the imaging member 10. With switch 25 closed, the electromagnet 29 isactivated so as to cause the ferrofluid to be attracted toward the topof the reservoir 22 where the fluid exits through the aperture 23 in thereservoir 22. As should be understood from the foregoing discussion, theapplication of a voltage to the ferrofluid causes ions to be transferredto the imaging surface.

As indicated hereinabove, a voltage bias is applied to the fluid mediain the fluid reservoir 22 via power supply 26 of the present invention.Typical voltages applied to the fluid media might range from about -4000V to about +4000 V, preferably between about +400 to about +700, andmore preferably ranging from about -600 to about -675 volts. The voltagethat is applied to the imaging member is essentially equal to thevoltage applied to the fluid media such that a voltage of 750 volts, forexample, applied to the ionically conductive medium results in a voltageof about 750 volts or slightly less on the imaging member. The voltageapplied to the fluid media 24 by the power source 26 can be of apositive polarity or a negative polarity wherein the polarity of thecharge which is deposited is exclusively controlled by the polarity ofthe voltage which is applied. The application of a positive bias to theionically conductive fluid medium 24 causes positive ions to transfer tothe imaging member while application of a negative bias to the ionicallyconductive fluid medium 24 causes negative ions to transfer to theimaging member.

Referring to FIGS. 1 and 2, the power supply of the present inventionconsist of belt 110 which is entrained about tension roller 114 anddrive roller 112. Drive roller 112 is coupled to a motor (not shown) bysuitable means such as a drive shaft. Belt 110 is maintained in tensionby a pair of springs (not shown) resiliently urging tension roller 114against belt 110 with the desired spring force. Roller 114 is rotatablymounted and rotates freely as belt 10 moves in the direction of arrow17. Belt 110 comprises a peripheral surface layer 14 of a piezoelectricpolymer film, such as polyvinylidene fluoride (PVDF) film, preferablyKynar® film manufactured by Pennwalt KTM, and preferably the belt isaluminized on the inside.

PVDF materials are formed by stretching the film in one direction, andapplying a large electric field to electrically polarize it in adirection perpendicular to the film. In FIG. 4, the stretch direction isdenoted by "1" and the polarization direction is denoted by "3". When aPVDF sheet is strained, it develops an internal electric field which isproportional to the deformation.

The present invention utilizes either a bimorph or a unimorph structurereferred to as a "Xeromorph" A bimorph Xeromorph consists of two PVDFsheets 102 and 104 laminated together with each sheet polarizationdirection opposed to each other having only a bottom electrode, as shownin FIG. 5. A unimorph Xeromorph consists of a single PVDF sheet 102laminated to a thick substrate 106 as shown in FIG. 6. The substratematerial may comprise materials which can be bent, and have nopiezoelectric properties.

Belt 110 is sufficiently elastic and resilient to deform around roller114. As belt 110 deforms around the radius of roller 114 an electricpotential is generated on the surface of belt 110 in the nip regionformed between conductive member 2 and belt 110. When the PVDF is passedover the smaller roller, the film is placed in tension on the outersurface and in compression on the inner surface. A high voltage(800-1500 V) is thus generated as the film is bent around the tightradius of the small roller. This voltage is then fed to charging device20 by belt 10, such as brush member or roller.

The manner in which the voltage is directed to the ionic charging devicedepends on the specific nature of the element. FIG. 3 shows the outersurface of the PVDF polymer coming into contact with an ionicallyconductive liquid in a reservoir. This is especially simple andadvantageous if the liquid is simply water because PVDF is completelychemically inert to water. Alternatively, the PVDF surface can becontacted with a carbon brush or roller which transfer the surfacecharge to the reservoir container or a wire placed into the reservoir.For example, the current requirement of ionomorphic charging device 20at 10 ips is calculated to be 90 microamps. This assumes 1000 V across a25 micron thick photoconductive member, a 14" wide panel and 100%efficiency. The current delivery capability of the PVDF film isproportional to the surface area of the film around the small roller,the rotation rate of the PVDF film, and the tension on the PVDF belt.Under reasonable rotation rates, surface areas and belt tensions, thepiezoelectric belt is capable of delivering sufficient power for ioniccharging. After traversing the small roller, a grounding roller 5 orbrush neutralize the charge on the piezoelectric surface.

It should be noted that unlike more conventional power supplies,however, the voltage is not set by external controls, but by the bendingstrain in the film. The practical limit for strain is controlled by boththe film thickness and the radius of the roller. If the roller had alarger radius, the field would be below its limit, while if the radiuswere smaller, the stretching might lead to degradation of the layer. Ifa larger roller had to be used, then the bilayer would have to be madethicker to generate the desired voltage, and at the same time care wouldbe needed in the mechanical design, to ensure that the belt did not passover sharper bends which would lead to excessive strain.

It is, therefore, apparent that there has been provided, in accordancewith the present invention, a power supply that fully satisfies the aimsand advantages set forth hereinabove. While this invention has beendescribed in conjunction with a specific embodiment thereof, it will beevident to those skilled in the art that many alternatives,modifications, and variations are possible to achieve the desiredresults. Accordingly, the present invention is intended to embrace allsuch alternatives, modifications, and variations which may fall withinthe spirit and scope of the following claims.

We claim:
 1. A power supply for transmitting voltage to a device,comprising:a web including a piezoelectric exterior layer for generatinga voltage on the surface thereof in response to being deformed; meansfor moving said web at a predetermined velocity in the direction ofmovement; and means for transferring the voltage on the surface of saidpiezoelectric exterior layer to the device.
 2. A power supply fortransmitting voltage to a device, comprising:a web including apiezoelectric exterior layer for generating a voltage on the surfacethereof in response to being deformed; a plurality of rollers, said webbeing entrained about said plurality of rollers to deform saidpiezoelectric exterior layer; and means for transferring the voltage onthe surface of said piezoelectric exterior layer to the device.
 3. Theapparatus of claim 2, wherein said piezoelectric exterior layercomprises a layer of piezoelectric polymer film.
 4. The apparatus ofclaim 2, wherein said piezoelectric exterior layer comprises:a firstlayer of piezoelectric polymer film having a first polarizationdirection; and a second layer of piezoelectric polymer film having asecond polarization direction opposed to the first polarizationdirection.
 5. The apparatus of claim 2, wherein one of said plurality ofrollers has a substantially different radii than another of saidplurality of rollers.
 6. A power supply for transmitting voltage to adevice, comprising:a web including a piezoelectric exterior layer forgenerating a voltage on the surface thereof in response to beingdeformed; and means for transferring the voltage on the surface of saidpiezoelectric exterior layer to the device and wherein said transfermeans includes a conductive brush coupled to said web.
 7. The apparatusof claim 6, wherein said transferring means includes a conductiverollercoupled to said web.